Photographic processes using silver halide have been in most widespread use because they give better photographic properties, such as sensitivity or gradation, than other photographic processes such as electrophotography or a diazo photographic process. In recent years, techniques that can give images easily and rapidly have been developed by changing the conventional wet treatment with a developer or the like in the formation and processing of images on photographic materials using silver halide to a dry treatment by, for example, heating.
Heat-developable photographic materials are known in the art, and the heat-developable photographic materials and processes therefor are described, for example, in Fundamentals of Photographic Engineering (Japanese language publication), pages 553-555 (Corona Co., 1979); Eizo Joho, page 40 (April 1978); Nebletts Handbook of Photography and Reprography, 7th ed. (Van Norstrand Reinhold Company), pages 32-33; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, RD No. 17029, June 1978, pages 9-15.
Many methods have been proposed with regard to the preparation of color images. With respect to the method of forming a color image by the coupling of an oxidation product of a developing agent with a coupler, U.S. Pat. No. 3,531,286 proposes a combination of a p-phenylenediamine reducing agent and a phenolic or active methylene coupler; U.S. Pat. No. 3,761,270, a p-aminophenol reducing agent; Belgian Pat. No. 802,519 and Research Disclosure, Vol. 137, September 1975, pages 31 and 32, a sulfonamidophenol reducing agent; and U.S. Pat. No. 4,021,240, a combination of a sulfonamidophenol reducing agent and a 4-equivalent coupler.
With regard to a method for forming a positive color image by the sensitized silver color bleaching process, useful dyes and the method of bleaching are described, for example, in Research Disclosure, RD No. 14433, April 1976, pages 30-33. Research Disclosure, RD No. 15227, December 1976, pages 14-15, and U.S. Pat. No. 4,235,957.
European Laid-Open Patent Publication Nos. 76,492 and 79,056 (corresponding to U.S. Pat. Nos. 4,500,626 and 4,483,914, respectively), and Japanese Patent Application (OPI) Nos. 15445/84 and 26008/83 (corresponding to U.S. Pat. No. 4,503,137) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") disclose a method for forming an image by heat-development utilizing a compound which has a dye moiety and at a high temperature, can release a mobile dye corresponding to, or inversely corresponding to, the reduction of silver halide to silver.
These heat-developable photographic materials are characterized by the fact that development is carried out by heating in a substantially water-free condition. Because of the dry processing, they have the great advantage of giving images easily and rapidly.
On the other hand, since necessary photographic reagents cannot be conveniently supplied from a developer solution, etc., all of the photographic reagents necessary for development should be included in advance in a photographic material. If the photographic reagents are added in an active form to the photographic material, they will tend to react with other components of the photographic material during storage before processing, or will decompose by the effect of heat, oxygen, etc., so that they cannot exhibit the desired performance during processing. One method for solving this problem is to block the active groups of the photographic reagents and add them in a substantially inactive form, namely, as precursors of the photographic reagents, to the photographic material.
A dye is one type of photographically useful reagent. If a functional group which greatly affects its spectral absorption is blocked to shift its spectral absorption to a shorter or longer wavelength side, the photographic material has the advantage that even when this dye is present together with a silver halide emulsion layer having a corresponding spectral sensitivity region, a decrease in sensitivity due to the so-called filter effect does not occur. If the useful photographic reagent is an antifoggant or a development restrainer, the action of such a reagent to decrease the sensitivity of the photographic material by its adsorption on the photosensitive silver halide or the formation of a silver salt during storage can be suppressed by blocking active groups thereof. By releasing these photographic reagents at required times, it is possible to reduce fogging without impairing sensitivity, inhibit overdevelopment fog, or to stop the development at a required time. If the useful photographic reagent is a developing agent, an auxiliary developing agent, or a fogging agent, blocking of active groups or adsorptive groups makes it possible to prevent various photographically deleterious actions due to the formation of semiquinone or oxidation products by air oxidation during storage, or to prevent the occurrence of a fog nucleus during storage by preventing electron injection into silver halide, and consequently to perform stable processing. If the photographic reagent is a bleach accelerator or a bleach-fixing accelerator its reaction with other components of the photographic material during storage can be inhibited by blocking its active groups. By removing the blocked groups during processing, the required performance of such reagent can be exhibited at required times.
Some techniques of blocking such photographic reagents have already been known in conventional photographic materials. For example, Japanese Patent Publication No. 44805/72 (corresponding to U.S. Pat. No. 3,615,617) utilizes blocking groups such as an acyl or sulfonyl group. Japanese Patent Publication Nos. 17369/79, 9696/80, and 34927/80 (corresponding to U.S. Pat. Nos. 3,888,677, 3,791,830 and 4,009,029, respectively) utilize blocking groups which release photographic reagents by the so-called reverse Michael reaction. Japanese Patent Publication No. 39727/79 (corresponding to U.S. Pat. Nos. 3,685,991, 3,674,478, 3,993,661 and 3,932,480), and Japanese Patent Application (OPI) Nos. 135944/82, 136945/82, and 136640/82 (corresponding to U.S. Pat. Nos. 4,416,977, 4,420,554 and 4,420,554, respectively) utilize blocking groups which release a photographic reagent by the formation of quinonemethide or quinonemethide-like compounds due to intramolecular electron transfer. Japanese Patent Application (OPI) No. 53330/80 (corresponding to U.S. Pat. Nos. 4,358,525 and 4,310,612) utilizes intramolecular cyclization reaction. Japanese Patent Application (OPI) Nos. 76541/82 (corresponding to U.S. Pat. No. 4,335,200), 135949/82 (corresponding to U.S. Pat. No. 4,350,752), and 179842/82 utilize cleavage of a 5-membered or 6-membered ring. All of these known techniques make use of hydrolysis or elimination of proton by the action of OH.sup..crclbar. during wet development. No precursor technology has yet been known in the case of dry processing using organic bases.